Genetic analysis of New World birds confirms untested evolutionary assumption

Biologists have always been fascinated by the diversity and changeability of life on Earth and have attempted to answer a fundamental question: How do new species originate?

by Jim Erickson

A phylogenetic tree of the 173 bird species in the study, colored according to the rates they produce species over deep time. Surrounding triangles depict the rate of population differentiation within each species. Image credit: Michael Harvey, PNAS

Biologists have always been fascinated by the diversity and changeability of life on Earth and have attempted to answer a fundamental question: How do new species originate?

An implicit assumption in the discipline of speciation biology is that genetic differences between populations of animals and plants in a given species are important drivers of new species formation and are a key to understanding evolution.

But that assumption has never been rigorously tested, until now, according to University of Michigan evolutionary biologist Michael Harvey, first author of a paper published online May 30 in Proceedings of the National Academy of Sciences.

Harvey and colleagues compiled and analyzed an unprecedented data set containing genetic sequences from 17,000 individuals in 173 New World bird species, ranging from ducks and owls to swallows and sparrows.

They demonstrated that species showing faster rates of genetic differentiation between populations are more likely to produce greater numbers of species over long evolutionary timescales.

"Our results are of fundamental significance because there are researchers across the world studying speciation, and many of them investigate genetic differences between populations that are in the process of forming new species," said Harvey, a postdoctoral fellow in the Department of Ecology and Evolutionary Biology, in the laboratory of Daniel Rabosky.

"These researchers assume those genetic differences are important for evolution, but this has never been shown in a satisfactory way. We are the first to show that the differences between populations studied by speciation biologists have been fundamental determinants of the formation of the diversity of life."